This photo was taken on August 14, 2003. It shows the night sky over Ontario, Canada, during a blackout.

This photo was taken on August 14, 2003. It shows the night sky over Ontario, Canada, during a blackout.

This photo was taken the next night. It shows how the night sky looks when there are many lights on.

This photo was taken the next night. It shows how the night sky looks when there are many lights on.

In Other Words

  • during a blackout when electricity was not available

Science Background

A lightbulb uses electricity to heat a thin strip of material that glows brightly. The material lasts a long time before it burns out. The glass bulb is filled with a mostly harmless gas.

Before You Move On

  • 1. Inference How is the sky in danger from human activity?

  • 2. Evidence and Conclusion How did astronomers first learn about light pollution?